# coding=utf-8
# Copyright 2018 Google AI, Google Brain and Carnegie Mellon University Authors and the HuggingFace Inc. team.
# Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
""" PyTorch Transformer XL model evaluation script.
    Adapted from https://github.com/kimiyoung/transformer-xl.
    In particular https://github.com/kimiyoung/transformer-xl/blob/master/pytorch/eval.py

    This script with default values evaluates a pretrained Transformer-XL on WikiText 103
"""
from __future__ import absolute_import, division, print_function, unicode_literals

import argparse
import logging
import time
import math

import torch

from pytorch_pretrained_bert import TransfoXLLMHeadModel, TransfoXLCorpus

logging.basicConfig(format = '%(asctime)s - %(levelname)s - %(name)s -   %(message)s',
                    datefmt = '%m/%d/%Y %H:%M:%S',
                    level = logging.INFO)
logger = logging.getLogger(__name__)

def main():
    parser = argparse.ArgumentParser(description='PyTorch Transformer Language Model')
    parser.add_argument('--model_name', type=str, default='transfo-xl-wt103',
                        help='pretrained model name')
    parser.add_argument('--split', type=str, default='test',
                        choices=['all', 'valid', 'test'],
                        help='which split to evaluate')
    parser.add_argument('--batch_size', type=int, default=10,
                        help='batch size')
    parser.add_argument('--tgt_len', type=int, default=128,
                        help='number of tokens to predict')
    parser.add_argument('--ext_len', type=int, default=0,
                        help='length of the extended context')
    parser.add_argument('--mem_len', type=int, default=1600,
                        help='length of the retained previous heads')
    parser.add_argument('--clamp_len', type=int, default=1000,
                        help='max positional embedding index')
    parser.add_argument('--no_cuda', action='store_true',
                        help='Do not use CUDA even though CUA is available')
    parser.add_argument('--work_dir', type=str, required=True,
                        help='path to the work_dir')
    parser.add_argument('--no_log', action='store_true',
                        help='do not log the eval result')
    parser.add_argument('--same_length', action='store_true',
                        help='set same length attention with masking')
    parser.add_argument('--server_ip', type=str, default='', help="Can be used for distant debugging.")
    parser.add_argument('--server_port', type=str, default='', help="Can be used for distant debugging.")
    args = parser.parse_args()
    assert args.ext_len >= 0, 'extended context length must be non-negative'

    if args.server_ip and args.server_port:
        # Distant debugging - see https://code.visualstudio.com/docs/python/debugging#_attach-to-a-local-script
        import ptvsd
        print("Waiting for debugger attach")
        ptvsd.enable_attach(address=(args.server_ip, args.server_port), redirect_output=True)
        ptvsd.wait_for_attach()

    device = torch.device("cuda" if torch.cuda.is_available() and not args.no_cuda else "cpu")
    logger.info("device: {}".format(device))

    # Load a pre-processed dataset
    # You can also build the corpus yourself using TransfoXLCorpus methods
    # The pre-processing involve computing word frequencies to prepare the Adaptive input and SoftMax
    # and tokenizing the dataset
    # The pre-processed corpus is a convertion (using the conversion script )
    corpus = TransfoXLCorpus.from_pretrained(args.model_name)
    ntokens = len(corpus.vocab)

    va_iter = corpus.get_iterator('valid', args.batch_size, args.tgt_len,
        device=device, ext_len=args.ext_len)
    te_iter = corpus.get_iterator('test', args.batch_size, args.tgt_len,
        device=device, ext_len=args.ext_len)

    # Load a pre-trained model
    model = TransfoXLLMHeadModel.from_pretrained(args.model_name)
    model = model.to(device)

    logger.info('Evaluating with bsz {} tgt_len {} ext_len {} mem_len {} clamp_len {}'.format(
        args.batch_size, args.tgt_len, args.ext_len, args.mem_len, args.clamp_len))

    model.reset_length(args.tgt_len, args.ext_len, args.mem_len)
    if args.clamp_len > 0:
        model.clamp_len = args.clamp_len
    if args.same_length:
        model.same_length = True

    ###############################################################################
    # Evaluation code
    ###############################################################################
    def evaluate(eval_iter):
        # Turn on evaluation mode which disables dropout.
        model.eval()
        total_len, total_loss = 0, 0.
        start_time = time.time()
        with torch.no_grad():
            mems = None
            for idx, (data, target, seq_len) in enumerate(eval_iter):
                ret = model(data, target, mems)
                loss, mems = ret
                loss = loss.mean()
                total_loss += seq_len * loss.item()
                total_len += seq_len
            total_time = time.time() - start_time
        logger.info('Time : {:.2f}s, {:.2f}ms/segment'.format(
                total_time, 1000 * total_time / (idx+1)))
        return total_loss / total_len

    # Run on test data.
    if args.split == 'all':
        test_loss = evaluate(te_iter)
        valid_loss = evaluate(va_iter)
    elif args.split == 'valid':
        valid_loss = evaluate(va_iter)
        test_loss = None
    elif args.split == 'test':
        test_loss = evaluate(te_iter)
        valid_loss = None

    def format_log(loss, split):
        log_str = '| {0} loss {1:5.2f} | {0} ppl {2:9.3f} '.format(
            split, loss, math.exp(loss))
        return log_str

    log_str = ''
    if valid_loss is not None:
        log_str += format_log(valid_loss, 'valid')
    if test_loss is not None:
        log_str += format_log(test_loss, 'test')

    logger.info('=' * 100)
    logger.info(log_str)
    logger.info('=' * 100)

if __name__ == '__main__':
    main()
